This invention pertains to methods of making polymer coated optical fiber.
Optical fibers typically are polymer coated to protect them against damage. During fiber manufacture and subsequent handling, it is necessary to maintain the interfacial bond between the (typically silica) fiber and the coating that contactingly surrounds the fiber. This coating is frequently referred to as the xe2x80x9cprimaryxe2x80x9d coating. A further coating that surrounds the primary coating is frequently referred to as the xe2x80x9csecondaryxe2x80x9d coating.
The interfacial bond between the fiber and the primary coating desirably is strong to prevent bond failure during fiber manufacture and subsequent handling. Such failure can result in the formation of a xe2x80x9cdelaminatedxe2x80x9d area which can adversely affect the optical performance of the fiber. A delaminated area is characterized by a gap at the interface of the fiber and the primary coating. The gap alters the mechanical properties at the point of delamination, and may cause fiber transmission losses. Even if the optical performance is substantially not affected, the presence of delamination can result in negative customer perception. Thus, the fiber/primary coating bond desirably should be robust.
On the other hand, during fiber installation and many other operations it is necessary to easily and cleanly remove the coating from a portion of the fiber. For this reason it is necessary that the fiber/primary coating bond strength be not too great.
Thus the strength of the fiber /primary coating bond is an important characteristic of an optical fiber. This strength can be expressed in terms of a delamination resistance. It will also be apparent that it would be highly desirable to have a simple, reliable method of determining the delamination resistance. Such a method could be used during fiber manufacturing as a quality control method, but could also be used during development of a new coating. Such a method, and apparatus that facilitates practice of the method, is described in U.S. Pat. No. 5,908,484 issued to Decker et al. on Jun. 1, 1999 and entitled xe2x80x9cMethod of Making A Coated Fiber . . . xe2x80x9d, which is incorporated herein by reference. The present invention is an improvement on the method and apparatus described in the Decker et al. patent.
The invention is a method of making a polymer-clad optical fiber that comprises a step of determining at a plurality of temperatures the delamination resistance of the polymer coating from the fiber.
The delamination resistance of the coated optical fiber is preferably measured at two different temperatures: advantageously at a temperature in the ambient range for fiber use (typically room temperature) and at an elevated temperature used in field stripping the fiber. The delamination resistance at ambient temperature can be compared with a predetermined target value for delamination resistance in use. The delamination resistance at elevated temperature can be compared with a predetermined lower target value for ease of strippability.
Coated optical fiber having delamination resistances outside the predetermined ranges will typically be rejected, but can be used in applications that have different delamination resistance requirements.